. A buffered solution is prepared containing acetic acid, HC₂H₃O₂, and sodium acetate, NaC₂H₃O₂, both at 0.5 M. Write a chemical equation showing how this buffered solution would resist a decrease in its pH if a few drops of aqueous strong acid HCI solution were added to it. Write a chemical equation showing how this buffered solution would resist an increase in its pH if a few drops of aqueous strong base NaOH solution were added to it.

Interpretation:

A chemical equation which shows how a buffer solution made from acetic acid and sodium acetate (both having concentrations of 0.5 M) tends to resist the pH changes upon addition of a strong base and a strong acid should be determined.

Concept Introduction:

The two key components in a buffer solution could be defined as the acid and its conjugate base or a base and its conjugate acid. Acetate buffer has acetic acid as the aid while sodium acetate or the acetate ion acts as the conjugate base of the acetic acid.

The preparation of the acetic acid buffer solution can be highlighted as below.

By mixing a weak acid with the salt that is produced by the reaction of the weak acid and a strong base. The two main components in this buffer system are the weak acid and the salt derived from the reaction of the same weak acid with a strong base.

An example of this kind of a buffer system is CH₃ COOH / CH₃ COONa buffer system (known as the acetic buffer system). These can give acidic pH values.

In general, among the two key constituents of a buffer solution, the salt would undergo complete dissociation to produce the ionized form of the salt. This ionized form of the salt is the component that reacts with the strong acid added.

In the acetic buffer system sodium acetate (CH₃ COONa) is the salt. It undergoes complete dissociation in aqueous media to produce acetate ion (CH₃ COO^- ) and sodium ions in aqueous media as indicated by equation (1)

The resultant acetate ions react with the strong acid [HCl] added as indicated by equation no (2)

According to equation (2) it is clear that the amount of HCl added reacts with acetate ions to produce acetic acid and chloride ions. The salt would provide enough acetate ions (CH₃ COO^- ) to react with HCl (remember that small amount would be added) hence it is clear that addition of HCl won’t change the amount of H+ in the medium. Therefore the pH of the medium is constant upon addition of a strong acid (small amount) in an acidic buffer solution...